Hi ArranJ - as wester said above, you can search for anything which has already been entered into the cookbooks in your bookshelf - recipe titles and tags at the moment. There's a search box on the home page when you're logged in, as well as the main page of your bookshelf. However, Cookbooker doesn't have an index of all the recipes in each book unless our members have entered them, and we don't have an index of ingredients (yet).
Cookbooker's content is user-generated, so that does mean there can be gaps, especially if you own cookbooks which haven't been reviewed much by other members. Every review which is added helps fill in the gaps, of course.
You might want to look at Eat Your Books, if you're looking for a straight index of cookbooks - they're at: www.eatyourbooks.com. They're not free, but they do have complete indexes of many cookbooks.